Cobalt Chloride-induced Hypoxia Modulates the Invasive Potential and Matrix Metalloproteinases of Primary and Metastatic Breast Cancer Cells

Background: Tumor hypoxia promotes cancer progression. Matrix metalloproteinases (MMPs) are required for breast cancer cell invasion. Materials and Methods: The effect of cobalt chloride (COCl2)-stimulated hypoxia on invasion potential and the expression of MMPs and tissue inhibitors of metalloproteinases (TIMPs) were investigated in four breast cancer cell lines, derived from primary sites (HCC1395 and HCC1937) and metastatic sites (MCF-7 and MDA-MB-231). Results: CoCl2-induced hypoxia induced HIF-1 alpha protein expression in all four cell lines. Hypoxia significantly increased the invasiveness of HCC1395 cells, which did not correlate with a change of any one MMP. Constitutive MMP expression was different between primary and metastatic breast cancer cells. MMP-2 and MMP-9 measured by RT-PCR and zymography were notably expressed in primary cancer cells but not apparent in metastatic ones. MMP-7 was also highly expressed in primary cancer cells. Hypoxia increased the expression of MMP-1, -10 and -13 in metastatic breast cancer cells, whereas only MMP-13 was up-regulated in primary HCC1937 cells by hypoxic stimulation. TIMPs were not altered by hypoxia, except for TIMP-4 which was down-regulated in MDA-MB-231 cells. Conclusion: This study demonstrated a cell line-specific effect of hypoxia on invasive potential and differential expression of constitutive MMPs in primary versus metastatic breast cancer cells, i.e. primary cancer cells expressed a wider range of MMPs, in particular MMP-2, -7 and -9, than the metastatic ones. The data suggest that MMPs play no crucial roles in hypoxia-induced tumor progression in primary breast cancer cells.